The one-sentence answer
Once your combined cross-border EU B2C sales pass €10,000, you have until the 10th day of the month after your first qualifying sale to register for OSS if you want that registration to apply retroactively from that sale — miss it and OSS only covers you from a later date, leaving the earlier sales to be sorted out under local VAT registrations in each destination country; and once you're in OSS, missing three consecutive quarterly returns after reminders can get you excluded from OSS (and IOSS) for two years.
This is a self-check aid, not tax advice. See the disclaimer at the bottom, and verify anything before you register, invoice, or rely on a deadline.
Situation 1 — you crossed €10,000 and haven't registered yet
Below €10,000 in combined cross-border EU B2C turnover you charge your own country's VAT and don't need OSS at all. The moment a sale takes your running total over €10,000, destination-country VAT becomes mandatory on your cross-border sales — and OSS is the one registration that lets you handle every country's VAT in a single return instead of registering in each one.
There's a specific window that decides whether OSS covers the sales you've already made:
- Register by the 10th of the month after your first qualifying sale → your OSS registration applies retroactively from the date of that first sale. Everything from the crossing point onward is covered by OSS. This is the clean outcome.
- Miss that date → your OSS registration only takes effect from the first day of the next calendar quarter. The cross-border sales you made between crossing the threshold and that later start date aren't covered by OSS — they have to be declared under a local VAT registration in each country where those customers were, at that country's rate.
Why the gap sales are the expensive part. It isn't a single "late fee". Uncovered sales mean you may owe destination-country VAT you never collected from the customer (so it comes out of your margin), plus the cost and hassle of a one-off VAT registration in each affected country. Any actual penalty or interest on top of that is set by the member state of consumption under its own rules — OSS itself doesn't levy a single EU-wide fine, so the exposure depends on which countries your gap sales landed in.
The practical takeaway: the day you see the calculator tip over €10,000, note the date of that sale — your retroactive window closes on the 10th of the following month.
On time vs. late: what changes
| Aspect | Registered within the window | Registered after the window |
|---|---|---|
| When OSS starts covering you | Retroactively, from your first qualifying sale | From the start of the next calendar quarter only |
| The sales made before that start date | All covered by OSS — one return | Fall to per-country local VAT registration in each destination country |
| VAT you may owe out of margin | None beyond what OSS collects — you charged destination VAT from the start | Destination VAT on the gap sales you didn't charge the customer |
| Penalties / interest | None for timing | Set by each member state of consumption, under its own rules |
| The fix | Nothing to fix | Register for OSS going forward and clean up the gap sales locally |
The single best way to never be in the right-hand column is to know the exact transaction that crossed €10,000 — which is the one thing the calculator is built to show you.
Situation 2 — you're already in OSS but fell behind on returns
This is the more serious kind of "late". OSS is a privilege, not a right: the tax authorities can exclude you from it for persistent non-compliance, and the bar is specific rather than discretionary.
- Late returns. If reminders to file have been issued for three consecutive return periods and you still haven't filed within 10 days of each reminder, you can be excluded from the scheme.
- Late payments. The same three-reminders-then-10-days pattern applies to payment: three periods of reminders, each unpaid within 10 days — unless the outstanding amount for a given return is under €100, which doesn't count toward exclusion.
- The two-year "quarantine". Exclusion isn't just for the scheme you tripped on. It applies a quarantine covering the eight quarters following the period in which you were removed — during which you can't use the OSS Union scheme, the OSS Non-Union scheme, or IOSS. In practice that means going back to registering and filing VAT country by country for two years.
A single late return isn't a catastrophe — the trigger is the consecutive, ignored-reminder pattern, not one missed deadline. But the cost of hitting the pattern (two years of per-country compliance) is high enough that filing something on time, even a nil return, is always worth it.
What to do right now
- Not sure whether you've crossed yet? Run your cross-border transactions through the €10,000 threshold calculator — it shows the exact sale that tips you over, so you know the date your retroactive window is counted from.
- Just realised you crossed? Your retroactive window closes on the 10th of the month after that first qualifying sale. Registering before then is the difference between "one OSS return" and "per-country cleanup".
- Wondering if you even need OSS? The SME exemption scheme can let some small sellers skip OSS and VAT collection entirely — worth checking before you register.
- Already in OSS and behind? File the outstanding returns (a nil return still counts) before the three-reminders pattern completes — that's what keeps you inside the scheme.
Sources
- Retroactive-registration deadline (10th of the following month), and what happens to earlier sales if you miss it — Sovos, "Union OSS — Don't be Late Registering for the EU VAT Scheme"; Marosa, "European VAT rules for e-commerce".
- Exclusion mechanics (three consecutive reminded periods, 10-day rule, the under-€100 payment carve-out, and the eight-quarter quarantine across OSS/IOSS) — Sovos, "OSS VAT Returns: Deadlines, Exclusions and Penalties"; amavat, "Penalties for late submission of OSS declarations".
- Penalties for late returns being set by the member state of consumption, and official filing/payment rules — the European Commission's "Declare and pay in OSS" page.
Disclaimer
This page and the calculator are a self-check aid, not tax advice or a filing system. Exact deadlines, penalty amounts, and exclusion procedures vary by member state and can change; the member state of consumption sets its own penalties for late or missing returns. Verify your own dates and obligations against the EU Commission's One Stop Shop portal or an accountant before registering, invoicing, or relying on any timing here.